Conventionally, a storage media library device contains a media drive unit which writes and reads data to and from a plurality of storage media such as magnetic tapes, magneto-optical disks, or the like, and a media storage unit which stores the plurality of storage media in predesignated positions in a media storage rack. The storage media library device also contains in its cabinet a robot which transports the plurality of storage media between the media drive unit and the media storage unit. The robot in the storage media library device is equipped with a detection device such as a CCD (Charge Coupled Device) used to read an identification code, such as a barcode attached to each storage medium, and to measure the relative positions of the robot with respect to the media drive unit and the media storage unit.
Based on the identification code read from each storage medium and the relative positions of the robot measured with respect to the media drive unit and the media storage unit by the detection device such as a CCD, the robot in the storage media library device is operated to take the storage medium from the media loading slot of the media drive unit and transport it for storing in the predesignated position in the media storage rack or to take the storage medium from the predesignated position in the media storage rack and transport it for loading into the media loading slot of the media drive unit (such operation will hereinafter be referred to as the storage media transport operation). The storage media transport operation of the robot is controlled by robot control firmware contained in the cabinet of the device. Various operations of the robot control firmware and storage media read/write operations of the media drive unit are centrally controlled by library control software in the host computer connected to the storage media library device. More specifically, the library control software issues to the robot control firmware a transport command for causing the robot to perform the storage media transport operation. The term “robot control firmware” used here refers to a combination of software and hardware necessary to control the complex mechanical components of the robot.
When a storage medium is being transported by the robot in the conventional storage media library device, if the storage media library device is subjected to vibrations due to the occurrence of an earthquake or the like, an error may occur in the action that the robot is performing to take the storage medium from the media drive unit or the media storage unit or to load or store the storage medium the robot is holding into the media drive unit or the media storage unit. If such an error occurs, the robot control firmware notifies the library control software in the host computer of an error. Upon reception of the error notification, the library control software instructs the robot control firmware to cause the robot to retry the same action (retry action). Then, the robot in the storage media library device tries to recover from the error that occurred during the transport of the storage medium, by performing the retry action a predetermined number of times in accordance with the instruction transferred from the robot control firmware.
When the vibration of the storage media library device caused by an earthquake or the like has subsided in a short time, the error recovery can be accomplished by causing the robot to perform the retry action such as described above. However, when the vibration of the storage media library device has persisted for a long time, if the robot is caused to perform the retry action the predetermined number of times, the storage media transport operation may not be completed normally. As a result, the chance of the storage media library device being caused to go down (i.e., to shut down), and hence the occurrence of a device down error, increases. When such a device down error occurs, a notification is sent to the library control software in the host computer, and the continued use of the storage media library device is rendered impossible under instruction from the library control software.
In this case, the storage media library device cannot be restored unless maintenance personnel (customer engineer (CE)) visits the place where the storage media library device is installed and repairs the storage media library device by replacing the affected unit(s) in the storage media library device and manually performing operations such as measuring the relative positions of the robot with respect to the media drive unit and the media storage unit. The problem is that the storage media library device needs maintenance/repair work carried out by maintenance personnel, which is time and labor consuming.
For reference purposes, Japanese Laid-open Patent Publication Nos. 56-93865 and 03-91157 will be presented below as prior art documents concerning prior art storage media library devices.
Japanese Laid-open Patent Publication No. 56-93865 discloses a cartridge access device for loading/unloading a magnetic tape cartridge and transporting it between a cartridge container and a magnetic recording/reading device by using an access mechanism, wherein the cartridge access device is equipped with a device for stopping the operation of the access mechanism upon detecting vibrations caused by an earthquake or the like. It is described that an accelerometer is provided as the device for stopping the operation of the access mechanism. However, in Japanese Laid-open Patent Publication No. 56-93865, no description is given as to the specific shape, mounting position, etc. of the accelerometer. Besides, in Japanese Laid-open Patent Publication No. 56-93865, no mention whatsoever is made of how the operation of the access mechanism is resumed by measuring the relative positions of the access mechanism with respect to the cartridge container and the magnetic recording/reading device and correcting any displacements in the relative positions after the vibrations caused by an earthquake or the like have subsided.
Japanese Laid-open Patent Publication No. 03-91157 discloses a control method for a cartridge library device comprising a recording/reproduction unit which records and reproduces data on a cartridge-type recording medium, an accessor robot which automatically retrieves a selected cartridge from a container means containing a large number of cartridges and stores a selected cartridge in the container means, and a means for detecting seismic levels, wherein when an earthquake occurs, if the seismic level is lower than a specified value, the operation of the accessor robot is temporarily stopped and is resumed after the earthquake has subsided, but if the seismic level is higher than the specified value, a device failure notification is sent to a host system. While it is described in Japanese Laid-open Patent Publication No. 03-91157 that a seismic sensor is used as the means for detecting seismic levels, no description is given as to the specific shape, mounting position, etc. of the seismic sensor. Besides, in Japanese Laid-open Patent Publication No. 03-91157, no mention whatsoever is made of how the operation of the accessor robot is resumed by measuring the relative positions of the accessor robot with respect to the recording/reproduction unit and the container means and correcting any displacements in the relative positions after the earthquake has subsided.
As a result, neither Japanese Laid-open Patent Publication No. 56-93865 nor No. 03-91157 can address the problems that occur when vibrations due to an earthquake or the like are encountered when a plurality of storage media such as magnetic tapes are being transported by the access mechanism or the accessor robot or the like using the prior art techniques.